While Justin Bieber was touring in Europe and getting into his own trouble there (including lunging at a big meanie paparazzo, passing out, having a terrible birthday and bailing on shows), his friends were busy disrespecting his property at home.

Lil Twist, 20, the same charmer who crashed Bieber's Fisker Karma into cement poles (after already doing a number on one of the singer's Ferraris), threw a party at Justin's house -- and had all sorts of illegal fun during it.

TMZ nabbed photos from the bash, which reportedly went down on March 19.

Twist and another pal who stayed with him while Bieber was across the pond is said to have invited 40 girls to the mansion along with a handful of dudes with which to share them. His hospitality included a hookah, plenty of alcohol and a whole lotta weed, which guests enjoyed under a large portrait of Bob Marley.

Sources say no neighbors complained. One partygoer said she left around 2AM and it was still going strong -- and so was the aroma of ganja in the Calabasas, Calif. pad.

Smells like teen (downward) spiral.